145/75R17 vs 155/65R17
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 145/75R17 | 155/65R17 | Change |
|---|---|---|---|
| Overall height | 25.6" | 24.9" | -2.5 % |
| Sidewall | 4.28" | 3.97" | -7.4 % |
| Section width | 145 mm | 155 mm | +6.9 % |
| Circumference | 80.3" | 78.3" | -2.5 % |
| Revs per mile | 789 | 809 | +2.5 % |
| Axle height | 12.78" | 12.47" | -8.0 mm |
| Approved rim width | 4–5.5" | 4–5.5" | overlap 4–5.5" |
Both are approved on a rim 4" to 5.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 145/75R17. Fit 155/65R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.3 mph | -1.7 |
| 90 mph | 87.8 mph | -2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,754 on the road, so it over-counts by 246. At a true 70 mph the first turns 920 times a minute, the second 944.